Pitch hits the ground

I hate to make this a semantics discussion, but read the rule. It says if they swing AFTER the ball hits the ground, it's dead ball and a ball awarded to the batter no matter the fact he/she swung. Now, what if the swing starts before the ball hits the ground? What I've been told in the clinics is that the play goes on, because it was swung at before the ball hit the ground. If the swing starts after the ball hits the ground, then the swing is ignored as if it never happened.